I got my PW three days ago and I must admit that my eyes hurt when reading in low light conditions with the light level set to 0. And when I lock my PW, it shows me the same page with no light for a moment and there is a lot of difference!

To developers: would it be possible to hack the PW in order to turn the light off when reading? Thank you!

In a well lit area, the PW light on one of the lower settings is virtually invisible (i.e. it sure looks like its off even though it isn't).

Agreed, also I'm pretty sure that in a lit room, with the PW light turned off, you are actually straining your eyes, because it's basically a black on grey, not that readable.
Eyestrain doesn't solely equal to how much light you put in your eyes. But also how difficult it is for you to read/see something. Also eyes needs some sun's light every day to stay healthy. It's not an all no light, or an all light.
You don't need high settings, but just having enought light so that it's a good black on white, is better, you just feel it that the minute you turn the light off (aka lowest setting), you are straining your eyes. Then would you want the display to be even grayer than it already is ? certainly not. The darker the background (closer to the text color) the more you strain your eyes. Why do you think they make paper white ? Pun intended.

There is no sensible reason to have an entirely turned off light except for saving energy/battery life/LEDs life
If you are reading on your paperwhite with the light at 0 or 1/24 in any light condition I think you are doing something wrong.

edit, & sry for long post: it all have to do with the environmental light also, if you are in a lit room, your eyes are "warmed up" and if you try to read/see something dark (like a Kindle 4 display with no light) > eye strain (nothing you can really feel but its there, because the display gray)
if you are in a dark room, your eyes are "cooled off", and will not be favorable to a lot of light, so you can't go all "paperwhite", but you need enough light to be able to do the reading part (difficulty of reading > eyestrain)
You have to factor everything. And at the end of the day, black out everything, and you can just feel it if you are confortable. If you feel that something is wrong, that point out that there is some low level of eye strain.

Give this device to an eye doctor, you'll see what he is gonna tell you.

You don't need high settings, but just having enought light so that it's a good black on white, is better, you just feel it that the minute you turn the light off (aka lowest setting), you are straining your eyes. Then would you want the display to be even grayer than it already is ? certainly not. The darker the background (closer to the text color) the more you strain your eyes. Why do you think they make paper white ? Pun intended.

The bold part (me) is a little misleading. It would appear that only too low contrast causes eye strain. Too much does no good either. I wish they would not make some paper so white. The paper we use at my work is that dang bleached perfect white paper. It is too bright for me - if it had the color and reflective properties of nice white styrofoam cups, I'd be happy. If reading in bright sunlight most paper is hard to read compared to the slightly grey background of e-ink - and that without having to use sunglasses. That is one thing e-ink is very good at, reading in sunlight, better than paper IMO, and certainly much better than any lcd ...

Eyestrain? Have you actually SEEN a Paperwhite on minimum light setting? Genuine question. I cannot imagine anyone getting "eyestrain" from the minimum light setting on a PW. It's a glimmer barely visible in a totally dark room.

I'm getting it.
If I read on the PW for a long time in the dark, my eyes ache. A lot.
It's like reading on an old laptop, to me.

I would have to agree that the PW does induce some eye-ache even at the lowest settings. For me, it's mainly because i find that the contrast suffers in a totally dark environment and i need to strain more to see the text.

As i increase the light, i find that the screen can become too bright and hurt my eyes.

Therefore, I find the best compromise is a very faint external room light, with PW set to about 4 on the scale.

During daytime, the PW clearly excels, with a whiter screen (setting 15)

There is no sensible reason to have an entirely turned off light except for saving energy/battery life/LEDs life
If you are reading on your paperwhite with the light at 0 or 1/24 in any light condition I think you are doing something wrong.

Are you an ophthalmologist? If not I see no qualification on your part to estimate the impact of an enabled LED light.

When I read in bed in complete darkness, I do get some eye strain from having the screen right in front of my face, even at levels 1-3. More so than with a book light. I still would not want to go back to a regular kindle and a booklight though. Just the stupid convenience of having a real book experience - open the cover, start ading, no buttons to push - and the PW's interface are worth the bit of eye strainto me.

I don't care about battery life or eye strain. I just like the ability to control everything my Paperwhite does. I'd like to be able to disable the light completely, and I'd like to be able to turn off the magnet sensor as well. No medical or economic reasons for this at all. I would just like complete dominion over my e-reader.

I don't care about battery life or eye strain. I just like the ability to control everything my Paperwhite does. I'd like to be able to disable the light completely, and I'd like to be able to turn off the magnet sensor as well. No medical or economic reasons for this at all. I would just like complete dominion over my e-reader.

You can't disable the magnet sensor. You can however turn the light off by using the magnet sensor as in Turn Off Frontlight W/O Jailbreak. For other ways to turn the light off, check out post #1, #6, and #62 in the thread that the linked post is in (all those require jailbreak and more).

For total dominion you have to get an open source ereader with documented and readily available source code. Good luck on finding one.

I just got my Paperwhite two days ago. It was a little difficult to get because I don't live in the USA. But I'm SO happy with it! The little LED lights are very easy on the eyes. Nothing like trying to read on my iPad, that hurt my eyes. And it's so nice to not have to clip a light onto it, like I have to do with my Sony.